JPH10211497A - Method for biological treatment of organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make organic sludge discharging outside a system be zero and COD of waste water-biologically treated-water hardly degrade by withdrawing a part of sludge in a biological treatment process, by circulating the part of the sludge between an aeration process and an ozone oxidation process, and then by returning the part of the sludge to the biological treatment process. SOLUTION: Waste water 1 is treated by a biological treatment process 2 and then sludge is withdrawn from a solid-liquid separation process 3 including a sedimentation layer. Withdrawn sludge 5 is introduced into a sludge-dissolving process. A part of the withdrawn sludge 5 is allowed to flow into an aeration treatment process 7 including another aeration tank separately from an activated sludge-aerating tank of the biological treatment process 2 and while aerated, the part of the withdrawn sludge 5 is allowed to circulate within an ozone treatment process 8 including an ozone-absorbing tank (ozone 10 is appropriately supplied). The amount of circulation of circulating sludge 9 circulating between the aeration treatment process 7 and the ozone treatment process 8 is set to be about 3 times the weight of SS equivalent to excess sludge generated. All of the circulating sludge 9 allowed to circulate is returned successively to the biological treatment process 2 as circulation treated sludge 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel process for biologically treating organic sewage such as sewage and industrial effluent, which eliminates the generation of excess sludge in the process of biologically treating sewage and industrial effluent, and which does not deteriorate the COD of biologically treated sewage. About technology.

[0002]

2. Description of the Related Art A large amount of organic sludge (excess sludge, raw sludge, etc.) is generated daily from activated sludge treatment facilities such as sewage, industrial wastewater, human waste, and landfill wastewater. Surpass. The treatment and disposal of this organic sludge is the biggest problem. Since this organic sludge is hardly dewaterable, a large amount of a dehydration aid (polymer, etc.) is added and dewatered with a sludge dewatering machine to a water content of about 85%, and the dewatered cake is landfilled or incinerated. However, there are many problems such as dehydration aid cost, insufficient landfill for dewatered cake, insufficient disposal place for incinerated ash, high incineration equipment cost, and high cost for heavy oil for incineration.

In order to solve such a problem, "Sludge reduction method using ozone" as shown in FIG.
06088. The technique described here supplies the organic wastewater 1 to the biological treatment step 22 and separates the biologically treated organic wastewater in the solid-liquid separation step 23 into a liquid component (treated water 4) and a solid component (returned sludge 26, The excess sludge is separated into excess sludge 25), and about three times the amount of the excess sludge out of the solid content is treated in the ozone oxidation step 27, and the ozone-oxidized sludge 28 is returned to the biological treatment step 22. The method described in this publication, from the activated sludge treatment step of wastewater,
This is a method in which an amount of activated sludge about three times larger than the amount of surplus sludge is drawn out, oxidized with ozone, and returned to the activated sludge treatment step as it is.

[0004]

However, the present inventor has conducted additional tests of the technique disclosed in the above-mentioned publication and found that there are the following drawbacks. When the ozone oxidized sludge is returned to the aeration tank in the sewage biological treatment process and biologically treated, part of the ozone oxidized sludge is certainly eliminated, but when the ozone oxidized sludge is aerated, a large amount of biodegradable COD is generated from the sludge. It was confirmed that the generated COD concentration of the treated water was significantly deteriorated. According to the experiment of the inventor, 1 kg of sludge that has disappeared
-It was found that about 120-140 g of COD was produced per SS. Since the sludge is oxidized with ozone, converted into BOD components, and returned to the aeration tank in the sewage treatment process, the BOD load in the aeration tank becomes high when there is not enough room in the aeration tank. When the load becomes high, the excess sludge generation rate in the sewage biological treatment process increases, and as a result, the required amount of ozone increases, leading to a vicious cycle of increasing running costs.

[0005] At present, when eutrophication of public water bodies is a major problem, the deterioration of the sewage effluent COD with the reduction of sludge is a major drawback of the prior art. In addition, it cannot be said that it is ideal unless it is a technology capable of obtaining good treated water quality. Therefore, the present invention overcomes the above-mentioned drawbacks of the conventional technology, and provides a new technology capable of reducing the amount of organic sludge discharged to the outside of a sewage treatment facility to zero, and in which the COD of sewage biological treatment water hardly deteriorates. Make it an issue.

[0006]

Means for Solving the Problems The present inventor has found that the above-mentioned problems can be solved by combining the method of oxidizing sludge with ozone and the biological treatment of sludge treated with ozone in a novel manner. That is, the present invention extracts a part of the sludge in the biological treatment step of the organic wastewater, circulates it between the aeration step provided separately from the biological treatment step, and the ozone oxidation step, and returns it to the biological treatment step. A biological treatment method for organic wastewater, characterized in that:

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described in detail with reference to FIG. In FIG. 1, a biological treatment step 2 including an activated sludge treatment (activated sludge aeration tank) for purifying wastewater 1 by aerobic microorganisms (a step of attaching an anaerobic part like a biological phosphorus removal method or a biological nitrification denitrification method) May be)
After that, sludge is extracted from the solid-liquid separation step 3 including the sedimentation layer, and the extracted sludge 5 is introduced into the “sludge elimination step” which is a feature of the present invention.

That is, a part of the extracted sludge 5 flows into an aeration treatment step 7 including an aeration tank separate from the activated sludge aeration tank in the biological treatment step 2, and is aerated while the ozone absorption tank (the ozone 10 is appropriately supplied). Treatment process 8)
Circulate between Here, the circulation amount of the circulating sludge 9 circulated between the aeration treatment step 7 and the ozone treatment step 8 is set to be about three times the SS weight equivalent to the generated excess sludge. In the present invention, the circulated sludge 9 is circulated in the biological treatment step 2.
It is desirable that all of the sludge is returned in turn as recycled sludge 11.

In this ozone treatment step 8, the circulating sludge 9 is oxidized by ozone and BOD capable of assimilating the sludge with microorganisms.
Convert to ingredients. In the aeration treatment step 7, when the ozone-oxidized sludge is aerated and subjected to aerobic biological treatment, a part of the ozone-oxidized sludge (biodegradability by microorganisms is improved by the oxidizing action of ozone) (30 to 40% of SS). ) Is decomposed into carbon dioxide and water by activated sludge (aerobic microorganisms) and disappears.

[0010] As described above, when the circulation treatment in which the ozone treatment step 8 and the aeration treatment step 7 are repeated is performed, the hardly biodegradable COD component generated when the ozone oxidized sludge is aerated and biologically eliminated is eliminated. Ozone is oxidized again, and the biodegradable COD is converted to the biodegradable COD by the oxidizing action of ozone.
Is repeated many times. As a result, surprisingly, the hard biodegradable C
It was confirmed that OD was highly degraded biologically.

On the other hand, in the prior art as shown in FIG. 2, the ozone-treated sludge is directly returned to the biological treatment tank in the sewage treatment step, so that the hardly biodegradable COD is generated from the ozone-oxidized sludge in the wastewater biological treatment tank. In addition, since the treated water flows out as it is, the COD of the sewage treated water is significantly deteriorated. On the other hand, in the biological treatment method according to the present invention, it has been experimentally confirmed that the amount of COD generated per 1 kg-SS of the sludge that has disappeared is about 1/8 of the conventional method, that is, about 15 g, which is remarkably reduced. .

[0012]

EXAMPLES Hereinafter, Examples and Comparative Examples of the present invention will be described.
The effect of the present invention can be made clearer. (Example) A verification test of the present invention was performed on sewage (average water quality is shown in Table 1) according to the process shown in FIG. Table 2 shows the test conditions.

[0013]

[Table 1]

[0014]

[Table 2]

As a result of the experiment, one month after the start of the treatment,
Conditions are stable, the final settling of the sewage biological treatment process
The average value of the treated water quality in the tongue tank is high as shown in column 1 of Table 3.
Each time, COD and BOD were removed. Therefore, the method of the present invention
Then, even if sludge disappears, COD deterioration of sewage treatment water is almost
Almost not. Sludge was tested for 6 months.
During the period, the sludge was not drawn out of the system, but
The MLVSS of the air tank was originally set at 3500-3700m
g / liter, the system outside the system of the present invention
It turned out that there was no generation of organic sludge
Was. Column 2 in Table 3 shows sewage treatment without sludge reduction.
It is the quality of the water. On the other hand, the normal activity without applying the present invention
The amount of excess sludge generated by the sludge method is 1 m of sewage. ^Three120 per
１３０130 g-SS.

[0016]

[Table 3]

(Comparative Example) As a result of operating according to the process diagram of the prior art (FIG. 2) using the same sewage and the same biological treatment process as that of the present invention, the COD of the sewage biological treatment water is shown in FIG.
It has deteriorated remarkably as shown in the column. The operating conditions of the prior art are as follows: Ozone oxidation of three times the amount of surplus activated sludge generation (ozone absorption amount of 0.05 to 0.08 g-ozone / g-) according to the description in JP-A-6-206088. SS) It is returned to the activated sludge treatment tank as it is.

[0018]

Thus, according to the present invention, the sludge extracted from the biological treatment tank for sewage is subjected to ozone treatment, and then the ozone oxidized sludge is subjected to biological treatment in an aeration tank separate from the aeration tank for sewage. As a result, the amount of organic sludge out of the system can be reduced to almost zero,
In addition, it is possible to provide a biological treatment method for organic wastewater in which the COD removal effect hardly deteriorates. Further, according to the present invention, after the ozone-treated sludge is aerated separately from the aeration tank for sewage to eliminate the sludge, the aeration tank for sewage treatment (biological treatment tank)
Therefore, it is possible to provide a biological treatment method for organic wastewater that does not cause a vicious cycle in which the wastewater biological treatment process as in the prior art has a high BOD load and increases the excess sludge generation rate.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a treatment step of an embodiment of a biological treatment method for organic wastewater according to the present invention.

FIG. 2 is a schematic view showing a conventional organic wastewater biological treatment method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sewage (organic sludge) 2 Biological treatment process 3 Solid-liquid separation process 4 Treated water 5 Sludge 6 Return sludge 7 Aeration treatment process 8 Ozone treatment process 9 Circulated sludge 10 Ozone 11 Circulated sludge

Claims (1)

[Claims] 1. A method for extracting a part of the sludge in a biological treatment step of an organic wastewater, circulating the sludge between an aeration step and an ozone oxidation step provided separately from the biological treatment step, and then returning the sludge to the biological treatment step. A biological treatment method for organic wastewater, comprising: